The present invention relates to a gas turbine, especially, for a combined cycle power plant.
In a gas turbine, a steam cooling system in which blades are cooled by steam in proportion as an inlet temperature of high temperature combustion gas increases, has been proposed. Especially, in a combined cycle power plant comprising an exhaust heat recovery boiler in which exhaust gas from the gas turbine is used as a heat source, the following steps have been proposed to improve the thermal efficiency of the gas turbine and the combined efficiency of the plant: generating low temperature steam for cooling, using the low temperature steam in the gas turbine for cooling a turbine blade, using the heated cooling steam in a steam turbine, and recovering the thermal energy. An example of such a conventional steam cooling structure of a gas turbine blade is shown in FIG. 3.
Cooling paths 5 and 7 are formed inside of a first stage stationary blade 1 and a second stage stationary blade 3, respectively, which are respectively connected to heads 9 and 11, and those heads 9 and 11 are connected to independent cooling steam supply pipes 13 and 15, and cooling steam recovery pipes 17 and 19. Those cooling steam supply pipes 13 and 15 are connected to an exhaust heat recovery boiler (not shown in FIG. 3) and the cooling steam recovery pipes 17 and 19 are connected to the low pressure turbine of the steam turbine via a separate superheater.
Furthermore, it has been proposed that the cooling steam flow in series with the cooling paths formed in each stage""s turbine blades (Japanese Patent Application, Second Publication, No. Sho 63-40244).
As aforementioned, in a steam cooling system in which the cooling steam flows in parallel to each stage""s stationary blades of the gas turbine in the steam turbine of the plant and is recovered, and also flows into the steam turbine, the above mentioned separate superheater is required in order to regulate the condition of the cooling steam, therefore, the power plant is complicated in structure, large, and its total cost is high.
Furthermore, when cooling steam flows in series to each stage""s stationary blades of the gas turbine in the steam turbine, the whole structure of the power plant is complicated, and the pressure drops due to the flow becoming large, so that heat recovery efficiency in the steam turbine tends to decrease.
In view of the aforementioned, an object of the present invention to provide a gas turbine for a combined cycle power plant wherein the cooling steam used for heat recovery has a small pressure drop and a special apparatus such as a superheater or the like for a steam turbine is not required.
To achieve the above object, the present invention provides a gas turbine for a combined cycle power plant comprising a steam cooled system having a gas turbine for generating steam for cooling in an exhaust heat recovery boiler to which exhaust gas from the gas turbine is supplied, and cooling the stationary blades with the steam for cooling; wherein the steam cooled system is constituted by connecting a cooling steam supply pipe from the exhaust heat recovery boiler to a cooling path formed in a first stage stationary blade, connecting a cooling steam recovery pipe connecting a steam turbine to a cooling path formed in a second stage stationary blade, and forming a cooling steam connecting path which has a relatively large cross-sectional area, to connect the cooling paths formed in the above first stage and second stage stationary blades.
The gas turbine for the combined cycle power plant of the present invention generates the steam for cooling in the exhaust heat recovery boiler to which the exhaust gas from the gas turbine is supplied and cools the stationary blades with the steam for cooling, wherein the cooling steam recovery pipe from the aforesaid exhaust heat recovery boiler is connected to the cooling path formed in the first stage stationary blade, the cooling steam recovery pipe connecting the steam turbine to the cooling path formed in the second stage stationary blade, and a cooling steam connecting path, which has a relatively large cross-sectional area, is formed to connect cooling paths formed in the above first stage and second stage stationary blades, so that the steam for cooling, which has flowed in the cooling paths in the first stage and second stage stationary blades, can be continuously used in the steam turbine as steam for cooling because the above steam for cooling has a suitable temperature to drive a medium-pressure turbine of the steam turbine and also the cooling steam connecting path has a relatively large cross-sectional area, and the pressure drop is as a whole small. Therefore, since no special apparatus such as a heating apparatus is required, and the steam for cooling is recovered and used, an increase in manufacturing cost can be avoided and also the efficiency of the combined cycle power plant can be improved.